Er40 collet chuck. I eventually got it clocked in with the dti reading 0.002mm runout and 0.004mm for the taper angle. Took hours to get compound set up!
First time using the big boring bar, makes a massive difference. Recut the taper but resulted in the bore being 1mm oversize.. had to face and shorten by 4.3mm to get it on size.
Also aquired a burnt ear thanks to the swarf.